Cytology is the branch of biology dealing with the study of the formation, structure, and function of cells. As applied in a laboratory setting, cytologists, cytotechnologists, and other medical professionals make medical diagnoses of a patient's condition based on visual examination of a specimen of the patient's cells. A typical cytological technique is a “Pap smear” test, in which cells are scraped from a woman's cervix and analyzed in order to detect the presence of abnormal cells, a precursor to the onset of cervical cancer. Cytological techniques are also used to detect abnormal cells and disease in other parts of the human body.
Cytological techniques are widely employed because collection of cell samples for analysis is generally less invasive than traditional surgical pathological procedures such as biopsies, whereby a tissue specimen is excised from the patient using specialized biopsy needles having spring loaded translatable stylets, fixed cannulae, and the like. Cell samples may be obtained from the patient by a variety of techniques including, for example, by scraping or swabbing an area, or by using a needle to aspirate body fluids from the chest cavity, bladder, spinal canal, or other appropriate area. The cell samples are often placed in solution and subsequently collected and transferred to a glass slide for viewing under magnification. Fixative and staining solutions are typically applied to the cells on the glass slide, often called a cell smear, for facilitating examination and for preserving the specimen for archival purposes.
A traditional multicolored stain is desirable for staining cell smears for certain cytological analyses. It is advantageous to stain the nucleus and the cytoplasm of the specimen with different colors, so that the nuclear material and cytoplasmic material can be readily distinguished either visually or by automated imaging equipment. In one staining practice, the cytoplasm is transparent, whereas the nucleus is transparent to opaque. This staining pattern allows the cytologist to distinguish cells which are morphologically abnormal indicated, for example, by nuclear material which is excessively large and/or dark in color. In addition, cytologists find the variety of colors of the traditional stains, particularly the Papanicolaou stain, helpful to reduce eye strain and to aid diagnosis.
Traditional stains, including the Papanicolaou stain, are difficult for an automated system to analyze. The variety of colors in the cytoplasm from traditional stains, which are straightforward for the human eye to distinguish, are not readily analyzed with automated imaging systems because they contrast to varying degrees with the traditional blue hematoxylin stain of the nucleus. The varying contrast makes automated analysis difficult.
During the approximately seventy years since its introduction, the original Papanicolaou stain has undergone many modifications. Currently, the dyes, reagents, and methodology vary widely based on the preferences of each laboratory. While standardization of a Papanicolaou-like stain has been proposed for many years, there has been little incentive for laboratories to do so. This variability affects current imaging technologies which may reject numerous slides either because of problems inherent with a conventional Pap smear preparation, or because of poor staining that produces nuclear-cytoplasmic contrast that is inadequate for image acquisition and analysis.
A number of researchers have developed algorithms in an attempt to attain automated analysis of cells stained with the multicolored Papanicolaou stain. Such techniques involve the use of various instrumental artifacts, such as different colors of light, filters, and color television cameras. Many require a high level of sophistication that is costly in terms of hardware and software.
Furthermore, the type of stain chosen may depend on the type of cells under examination, as well as the specific abnormality or disease to be diagnosed. For this reason, various stains may be used in various laboratory settings.
Conventional machine vision illumination sources are low efficiency broadband sources such as tungsten-halogen, sodium-halide, or xenon lamps. These sources convert a small percentage of their input energy to broadband light. Accordingly, efficiency drops significantly in a cytological application that requires a narrow band light source. Typically, these devices generate a significant amount of heat, require filters for obtaining correct wavelengths, and are relatively large.
There, thus remains a need for an improved light source for illuminating a biological specimen carried by a microscope.